A lamination structure includes a flat or fluted layer bonded to a flat layer or a fluted layer with a starch adhesive. At least one of the bonded surfaces may be a plastic surface.
Corrugated structures, such as cardboard and corrugated board structures, are described in the Finestone, et al. U.S. Pat. No. 6,083,580 (Finestone ""580 patent).
Corrugated board products are used extensively for a wide range of packaging applications. Thus, most shipping cartons are fabricated of corrugated paperboard. In its fundamental form, corrugated paperboard is composed of a fluted paper core sandwiched between and bonded to inner and outer paper face liners.
Corrugated paperboard is usually fabricated of natural brown-color kraft paper, although some boards include an outer liner of white or coated paper, or other suitable material, depending on the finish desired. The choice of a finish liner must take into account that it is often the practice to label the board with printed data, or to apply decorative graphics thereto; hence the outer face liner must be receptive to printing inks. It is also desirable that the outer face liner render the board water resistant. The manner in which corrugated paperboard is manufactured is described in U.S. Pat. No. 5,147,480 to Lang. In this patent the outer face liner of the board is identified as a xe2x80x9csingle liner,xe2x80x9d the inner face liner is referred to as the xe2x80x9cdouble liner,xe2x80x9d while the fluted core is called the xe2x80x9ccorrugated medium.xe2x80x9d
As noted in the Lang patent, the conventional technique for manufacturing corrugated paperboard makes use of a single facer unit and a double backer glue machine. In the single facer unit, a single face liner from a take-off roll is fed into the unit. A web of the medium to be corrugated is drawn from another take-off roll and fed through cooperating corrugator rolls. The resultant fluted or corrugated medium has adhesive applied to hereto before it is combined with the single face liner.
Thus, coming out of the single facer unit is a laminate web formed by the single face liner combined with the fluted medium. This laminate web is fed into the double backer glue machine where it is glued to a web of double liner drawn from a take-off roll.
Hence, emerging from the double backer glue machine is a continuous web of corrugated paperboard in which the fluted medium or core is sandwiched between and bonded to inner and outer face liners. This web immediately goes through a curing step, which cures the adhesive bond between the outer face liner and the fluted medium. The corrugated paperboard web is then slit, scored, and cut to provide corrugated paperboard having the desired carton specifications.
The structural strength and wearing properties of corrugated paperboard is in part determined by the face liners. Thus, when a shipping carton is made of corrugated paperboard whose outer face liner is kraft paper, this carton will not be water resistant and exposure to rain and snow in the course of shipment may weaken the carton.
Corrugated paperboard is likewise used to form inexpensive furniture items, such as storage units, shelving, and tables. Although these items have the advantage of being light-weight and inexpensive, they are subject to damage such as bending, creasing, and tearing. When such products are used in or near an area where water is present, water damage tends to destroy the appearance and, eventually, the structural integrity of the furniture item. There is thus a need for a cardboard material that can be used to form strong structures and containers wherein the cardboard also has the ability to resist water and other fluid damage.
Plastic film may be laminated to the outside surface of the finished cardboard in order to make it water resistant and also to enhance the appearance of the cardboard, such as, for example, by the application of decorative plastic film. A protective coating of wax or polyethylene may also be applied to the outside surface of a finished cardboard product.
In the Finestone ""580 patent, it is stated that a typical prior art method of laminating plastic film to corrugated paperboard is to attach the film to the outer face liner of the finished corrugated paperboard, during an off-line process on separate laminator equipment. That is, lamination does not take place at the xe2x80x9cprocess endxe2x80x9d of the production line where the inner and outer face liners are adhered to the fluted medium. Instead, prior art methods of applying a plastic film laminate layer wait until after the fluted core has been sandwiched between paper face liners and the adhesive holding this xe2x80x9csandwichxe2x80x9d has cured. The separate steps involved in such lamination processes add greatly to the cost of the laminated product, by increasing scheduling difficulties in the manufacture of different production runs, and by producing a higher percentage of waste material. Additionally, the Finestone ""580 patent states that flexible plastic film material is slippery and tends to shrink when heated, making it more difficultxe2x80x94and therefore more costlyxe2x80x94to work with. Furthermore, the nature of the film may be such as to preclude printing of the outer liner with standard printing inks.
In the Finestone ""580 patent, it is further stated that prior art attempts to apply plastic film laminates to cardboard face liners have met with the most success by applying the laminate after the corrugated paperboard has been fully formed, such as in the Lang U.S. Pat. No. 5,147,480. Unsuccessful attempts have been made to make outer face liners out of plastic film laminates and to apply these laminated outer face liners directly to the fluted medium. In the Finestone ""580 patent, it is stated that these attempts have been unsuccessful, as noted in Lang (col. 16, lines 18-25), because when the plastic film outer face liner is glued to the fluted medium, it is immediately subjected to heat and pressure in order to cure the bond between the outer face liner and the fluted medium. The heat and pressure degrade the plastic film laminate""s appearance and other properties. In particular, the fresh, wet adhesive between the plastic film laminate and the fluted medium tends to cause slippage as the corrugated web enters the curing step. Slippage causes unwanted misalignment and unevenness in the surface texture of the finished product. Additionally, the heat that is applied in the curing step tends to cause the plastic film layer of the laminate to shrink.
The Finestone ""580 patent states that these problems of slippage and shrinkage of the plastic film, which have not been overcome in the prior art, are addressed and resolved by the invention described in the Finestone ""580 patent. Additionally, the Finestone ""580 patent states that the invention described therein addresses the need for a low-cost cardboard material that is used to form containers and other structural members that are inexpensive, light-weight, and capable of withstanding heavy loading and impact forces as well as direct contact with water and other fluids.
The Finestone ""580 patent describes a container having walls made of a paper/plastic laminate to impart strength and rigidity to the container and to render it capable of resisting damage due to exposure to water and other fluids. The paper side of this laminate is bonded to the paper surface of a fluted layer in this container.
The Olvey U.S. Pat. No. 5,772,819 also describes a container having walls made of a paper/plastic laminate. At column 7, lines 22-25 of this Olvey patent, it is stated that the paper side of this laminate is bonded to the flute tips of a fluted layer.
A lamination structure comprises a first layer bonded to a second layer. At least one of the first layer and the second layer comprise a thermoplastic film. The first layer is bonded to the second layer by a destruct bond with a starch adhesive. The first layer may be a flat layer or a fluted layer and the second layer may be a flat or fluted layer. At least one surface of the first layer and/or the second layer, which is bonded to the other layer, is the surface of a thermoplastic film. The thermoplastic film is treated or coated in a manner sufficient to permit the surface or surfaces to form the above-mentioned destruct bond, using a starch adhesive.
A paper and plastic structure comprises an inner face liner, an outer face liner and a cardboard core. At least one of the inner face liner, the outer face liner and the cardboard core comprise a thermoplastic film. The inner face liner and the outer face liner are bonded to the cardboard core by destruct bonds with a starch adhesive. At least one surface of the inner face liner, the outer face liner or the cardboard core, which is bonded to the starch adhesive, is the surface of a thermoplastic film. The surface of the thermoplastic film is treated or coated in a manner sufficient to render this surface of the thermoplastic film capable of bonding with the starch adhesive in a destruct manner.
As indicated in the Finestone et al. U.S. Pat. No. 6,083,580, particularly with reference to FIG. 5 therein, the cardboard core may be a planar stiff paper core. This cardboard core may also be a planar stiff plastic core or a planar stiff paper/plastic composite core. Preferably, however, the cardboard core has a fluted or corrugated structure.